A. ETSI and INAP
The European Telecommunications Standards Institute (ETSI) has developed the Intelligent Network Application Protocol (INAP), now called the ETSI Core INAP. The Core INAP includes the essential capabilities of the INAP specification needed to support Intelligent Network (IN) service deployment.
To implement the Core INAP on conventional telephone routing and control circuits for North American telephone systems requires modification. The standard equipment must be more flexible.
B. Telephone Number Components
For example, in North America, the first three digits of a ten-digit telephone number -normally designate an Area Code (also called NPA) or a Service Code (such as 800); the next three digits represent an Exchange or Central Office Code (also called an NNX or NXX); and the final four digits represent a specific line within the NPA-NXX.
Outside of North America, telephone numbers often have different lengths and formats. Although such telephone numbers may also have leading digits to designate an area, these "Area Codes," or "City Codes" as they are sometimes called, often have different lengths. Also, the format and content of telephone number parameters vary, and have different dialing scenarios, as does the terminology describing the different parameters. To reduce confusion, this description will use the following terms to refer to different telephone number components.
The term "National Significant Number" refers to a fully qualified subscriber number containing a subscriber's Dialing Area Code and Local Subscriber Number. The "Dialing Area Code" identifies different geographical areas in the telephone network, just as the North American NPA does. The "Local Subscriber Number" is the number dialed to access a subscriber in the same dialing area as the caller.
The term "National Dialing Prefix," sometimes called the "Trunk Prefix," is used to dial in-country Iona distance calls. The National Dialing Prefix is present when the Nature of Address (NOA) value is a "Subscriber" value. The term "National Operator Selection Code," sometimes called the "Carrier Selection Code," refers to digits dialed before the National Dialing Prefix and National Significant Number to select a long distance carrier. The term "International Prefix" or "International Operator Selection Code" refers to digits dialed before a Country Code and National Significant Number to select an international carrier. For some Network Operators, the International Operator Selection code also serves as the International Dialing prefix. There are also other special or miscellaneous numbers. One example is a Service Code to provide 800-like services.
In light of the foregoing, there is a need for telephone switching networks to recognize and respond to telephone numbers from several different countries, and to give telephone switching equipment the flexibility to adapt to different telephone number formats.